Field of the Invention
The invention relates to aircraft gas turbine engine two dimensional vectoring nozzles and, particularly, for such nozzles designed to block line of sight through the nozzle's exit.
High performance military aircraft typically include a turbofan gas turbine engine having an afterburner or augmenter for providing additional thrust when desired and some are being developed with two dimensional vectorable nozzles. The turbofan engine includes in downstream serial flow communication, a multistage fan, a multistage compressor, a combustor, a high pressure turbine powering the compressor, a low pressure turbine powering the fan, and the nozzle. During operation, air is compressed in turn through the fan and compressor and mixed with fuel in the combustor and ignited for generating hot combustion gases which flow downstream through the turbine stages which extract energy therefrom. The hot core gases are then discharged into an exhaust section of the engine which includes an augmenter from which they are discharged from the engine through the nozzle which is also typically variable area exhaust nozzle.
One type of two dimensional nozzle is a single expansion ramp nozzle referred to as a SERN nozzle. SERN was developed as a variable area non-axisymmetric nozzle with a unique installed performance characteristic of low weight and frictional drag because there is no or a smaller lower cowl. Low observable (LO) exhaust nozzle technology is being developed for current and future fighter/attack aircraft. LO nozzles should be integrated cleanly with the aircraft airframe and not degrade the aircraft's performance due to weight and drag penalties. Exhaust systems for combat aircraft should possess characteristics to enhance aircraft survivability, including high internal performance, reduced radar cross section (RCS), low infrared (IR) signatures, low installed weight, low installation drag and, in some cases, thrust-vectoring capabilities.
Two dimensional nozzles have been developed for the purpose of accomplishing thrust vectoring. Two dimensional vectorable exhaust nozzles incorporate upper and lower flaps that are angled simultaneously for the purpose of deflecting exhaust gas in an upward or downward direction. Increasing the angle of the flaps increases the amount of turning that is imparted to the exhaust gas flow.
The augmenter includes an exhaust casing and liner therein which defines a combustion zone. Fuel spraybars and flameholders are mounted between the turbines and the exhaust nozzle for injecting additional fuel when desired during reheat operation for burning in the augmenter for producing additional thrust. In a bypass turbofan engine, an annular bypass duct extends from the fan to the augmenter for bypassing a portion of the fan air around the core engine to the augmenter. The bypass air is used in part for cooling the exhaust liner and also is mixed with the core gases prior to discharge through the exhaust nozzle. Turbojets, engines without bypass ducts may also use augmenters and variable area two dimensional nozzles.
Various types of flameholders are known and typically include radial and circumferential V-shaped gutters which provide local low velocity recirculation and stagnation regions therebehind, in otherwise high velocity core gas flow, for sustaining combustion during reheat operation. Since the core gases are the product of combustion in the core engine, they are initially hot when they leave the turbine, and are further heated when burned with the bypass air and additional fuel during reheat operation.
The hot parts of the engine visible along lines of sight through the exhaust nozzle produce an infrared signal or signature. The rotating turbine has a radar detectable signature or radar cross section (RCS). This invention relates to apparatus for reducing the engine's radar cross-section and suppressing and masking infrared (IR) emissions through engine exhaust ducts particularly those due to turbine and augmenter parts. Successful operation of combat aircraft is dependent, in part, upon the ability of the aircraft to remain undetected by infrared sensors and radars of missiles during flight. The high temperatures of the engine's exhaust gases and the hot metal turbine parts and the hot metal walls directly in contact with the hot gases cause the engine to emit high levels of infrared energy. Military aircraft engaged in combat are vulnerable to anti-aircraft missiles employing highly sophisticated infrared sensors and radar.